Liquid-liquid extraction, also referred to as solvent extraction or partitioning, is a method used in hydrometallurgy to separate or extract compounds from one liquid phase into another liquid phase. This is accomplished by manipulating the relative solubilities of the compounds to be isolated in two or more liquids having differing characteristics, as is the case with an aqueous phase (such as water), and an organic solvent phase (such as an oil or immiscible organic solvent).
The term ‘solvent extraction’ can also refer to the separation of a substance from a mixture by preferentially dissolving that substance in a suitable solvent. In such a case, a soluble compound may be separated from an insoluble compound or a complex matrix.
Although the term ‘partitioning’ is sometimes used to refer to the underlying chemical and physical processes involved in liquid-liquid extraction, these terms as used herein may be considered synonymous.
In the field of solvent extraction, several hydrometallurgical systems have in the past been developed which incorporate systems for manipulating liquid flow streams and phases, and for separating, splitting, or isolating liquids or phases of liquids, and the desired compounds extracted by such systems. Typically, a mixture of an extractant in a diluent is used to extract a desired compound from one phase to another. In solvent extraction techniques this mixture is often referred to as the organic phase and entrained organics need to be removed or recovered from the eventual aqueous streams.
Many extraction processes make use of so-called mixer-settlers. Mixer-settlers are a type of mineral process equipment used in solvent extraction processes and which consist of a first stage that mixes the phases together in an agitated tank (referred to as a mixer) followed by a quiescent settling stage, usually in the form of a gravity settling basin or tank (settler) that allows the phases to separate by gravity. It is difficult to manage the flow of liquid in settlers to achieve sufficient separation of the various liquid phases and to minimise the settler area that is required to effect separation of the phases. The flow of liquids needs to be as laminar as possible, as flow interruptions or turbulence can lead to co-mixing of phases and resultant losses in extraction efficiency. The settling stage allows the phases to separate, but achieving high flow rates can disturb the flow and hamper the process of separation, making it inefficient. Such systems are analysed using so-called CFD (computational fluid dynamics) modelling.
In conventional systems of which the Applicant is aware, adequately sized and positioned feed distribution baffles are positioned in the feed streams in the settler area in an attempt to effect an even flow, but these systems do not produce a suitably even distribution of fluids at higher velocities. A common problem with such baffles is that they are highly susceptible to scaling, leading to significant down-time and process interruption for cleaning or replacement of baffle elements. Other systems that the Applicant is aware of include fixed obstacles or deflector plates placed within the settler area but these systems have significant drawbacks in terms of settler kinetics and flow dynamics. So-called split launders and variable-split launders have also been used in certain systems, but these are also of little value in ensuring smooth fluid flow and dispersion distribution.
There exists a need for a settler dispersion distribution array which addresses some of the shortcomings of the prior art.
The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement nor admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
Throughout the specification and claims, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. The term “linearly spaced” or derivatives thereof are to be understood to refer to the spacing apart of two or more items along their length so as to create a ‘line’ of those items.
The term “re-entrainment prevention apparatus” or variations thereof will be understood to refer to a feed distribution array provided in a form so as to accord with the present invention. That is, the “re-entrainment prevention apparatus” of the present invention is a form of feed distribution array. Additionally however, the “re-entrainment prevention apparatus” of the present invention also incorporates therein a portion thereof that is accurately defined as a feed distribution array. The specifics of this arrangement will be described hereinafter.